A defoamer or antifoam agent is a material which, when added in low concentration to a foaming liquid controls the foam problem. Such materials, in addition, remove unsightly and troublesome surface foam and improve the filtration, watering, washing, and drainage of various types of suspensions, mixtures, and slurries. Defoamers have found application traditionally in such areas of use as the pulp and paper industry, paints and latex, coating processes, fertilizers, textiles, fermentation processes, metal working, adhesive, caulk and polymer manufacture, the sugar beet industry, oil well cement, cleaning compounds, detergents, cooling towers, and in chemical processes of varied description such as municipal and industrial primary and secondary waste water treatment.
It is essential for a defoamer that it be inert and not capable of reacting with the product or system in which it is used, and that it have no adverse effect on the product or system. A silicone antifoam agent is favorable, because it is chemically stable, rarely affects the treatment process, and exhibits a relatively high antifoam effect even in small amounts.
The use of various silicone containing compositions as antifoams or defoamers is known. In this regard, it is well established that this art is highly unpredictable and slight modifications can greatly alter the performance of such compositions. Most of the compositions contain silicone fluid (usually dimethylpolysiloxane), often in combination with small amount of silica filler. Many silicone foam control agents are known to suppress foam.
For example, Sullivan, in U.S. Pat. No. 3,383,327, discloses an antifoam agent prepared from a polydiorganosiloxane fluid, silica, and a hydroxylated polydimethylsiloxane. Rauner, in U.S. Pat. No. 3,455,839, discloses an aqueous defoaming composition consisting essentially of a polydimethylsiloxane fluid, a resin composed of (CH.sub.3).sub.3 SiO.sub.1/2 units and SiO.sub.2 units and a silica aerogel.
Raleigh et al., in U.S. Pat. No. 4,012,334, disclose an antifoam composition comprising a dimethylpolysiloxane and a precipitated silica reacted with hexamethyldisilazane and a process for the preparation and use thereof. Edward, in U.S. Pat. No. 4,145,308, discloses foam suppressant compositions, useful in both aqueous and hydrocarbon liquids, consisting essentially of a polydimethylsiloxane, a silicone resin comprised of R.sub.3 SiO.sub.1/2 units and SiO.sub.2 units wherein R is a monovalent hydrocarbon radical, and fumed or precipitated silica.
Maloney et al., in U.S. Pat. No. 4,443,357, disclose a foam controlling composition consisting essentially of an organopolysiloxane having at least one terminal alkoxy or hydroxy group, an organic silicone compound having the general formula R.sub.2 SiZ.sub.2 wherein R is a monovalent hydrocarbon group and Z is a hydrolyzable group containing nitrogen, and silica. Pape et al., in U.S. Pat. No. 4,486,336, disclose foam suppressant compositions consisting essentially of a low viscosity polydimethylsiloxane, a high viscosity polydimethylsiloxane, a silicone resin comprising (CH.sub.3).sub.3 SiO.sub.1/2 units and SiO.sub.2 units, and silica.
John, in EP 0 217 501 teaches a foam control composition having a liquid siloxane component having a certain viscosity and a liquid siloxane component obtained from a triorganosiloxane-endblocked polydiorganosiloxane, a polydiorganosiloxane having at least one terminal silanol group and an organosiloxane resin. Keil, in GB 1 505 655 teaches the use of silicone glycol molecules as defoamers. A process for controlling foaming in highly acidic aqueous systems using a silicone foam control agent is disclosed in U.S. Pat. No. 4,762,640. The foam control agent consists essentially of (A) a dimethylpolysiloxane gum having a viscosity greater than 150,00 Poise at 25.degree. C. and (B) a non ionic surfactant, (C) a siloxane copolymer dispersing agent and, optionally, (D) water. Additionally, other anti-foaming agents are disclosed in JP 87318582.
In Fey, U.S. Pat. No. 4,554,331, it is taught that certain compositions can be produced from reactive liquid resins and a compound selected from acyloxysilanes, alkoxysilanes, and oximosilanes. U.S. Pat. No. 5,091,484 to Colas teaches the use of hydroxyl, trialkoxy, or alkylene-trialkoxy end-blocked polydiorganosiloxane and a special MG resin.
Aizawa et al., in U.S. Pat. Nos. 4,639,489 and 4,749,740 teach a method for producing a silicone defoamer composition wherein a complex mixture of polyorganosiloxanes, filler, a resinous siloxane, and a catalyst, to promote the reaction of the other components, are heated together at 50.degree. C. to 300.degree. C.
Hydrophobed silica/polydimethylsiloxane antifoams are also reviewed in DEFOAMING: Theory and Industrial Applications; Garrett, P. R., Ed.; Surfactant Science Series 45; Marcel Dekker: New York, 1993, especially pages 246-249.
Additionally, these silicone antifoam agents may include various surfactants and dispersing agents in order in impart improved foam control or stability properties to the compositions. Thus, for example, Rosen, in U.S. Pat. No. 4,076,648, teaches self-dispersible antifoam compositions consisting essentially of a lipophilic nonionic surface active agent homogeneously dispersed in a non-emulsified diorganopolysiloxane antifoam agent. This combination is said to promote dispersability in water without the need for emulsification.
Keil, in U.S. Pat. No. 3,984,347, discloses a composition for controlling foam which comprises (1) a base oil of polyoxypropylene polymers, polyoxypropylene-polyoxyethylene copolymers or siloxane glycol copolymers, (2) an antifoam agent comprising a liquid polydimethylsiloxane, silica, and optionally a siloxane resin and (3) a siloxane copolymer dispersing agent. This composition enables the introduction of a diluted antifoam agent without having to make a water based emulsion.
McGee et al. in European Patent Application No. 341,952 disclose a foam control composition comprising (I) a silicone defoamer reaction product and (II) a silicone glycol copolymer, which is disclosed as being particularly effective in defoaming highly acidic or highly basic aqueous systems. However, when a foam control composition comprising a silicone antifoam agent and a silicone glycol copolymer is employed it is added in the form of a liquid or after dilution with water to a foamable liquid thus requiring higher levels of the silicone copolymer.